1. Field of the Invention
The present invention relates to a signal processor and cooling method of the same, and a radio receiver including the signal processor and cooling method of the same, more especially to a radio receiver that receives a desired signal while cooling a high frequency receiving section, which is applied to a base station radio device for mobile communication, satellite communication, or the like, and a cooling method thereof.
The present application claims priority of Japanese Patent Application No.2000-362233 filed on Nov. 29, 2000, which is hereby incorporated by reference.
2. Description of the Related Art
FIG. 2 is a block diagram showing a basic constitution of a conventional radio receiver. Description will be made as follows based on the FIG. 2.
The conventional radio receiver includes: an antenna terminal 1; a band-pass filter 2 that selects a predetermined signal from a receiving signal input from the antenna terminal 1; a low noise amplifier 3 that amplifies an output from the band-pass filter 2 to a predetermined level with low noise; and a receiving signal output terminal 4 that outputs the receiving signal amplified in the low noise amplifier 3. Further, the band-pass filter 2 and the low noise amplifier 3 are vacuum-sealed in a vacuum vessel 5, which are vacuum insulated to the outside by a vacuum insulation layer 6 and cooled on a cooling stage 8 by a refrigerator 7. Moreover, the radio receiver is further provided with: a first power source terminal 9 that supplies operating power to the low noise amplifier 3; and a second power source terminal 10 that supplies operating power to the refrigerator 7. The vacuum vessel 5 and the refrigerator 7 are housed in a case 11.
The vacuum vessel 5 blocks heat entering from the outside with a structure where the inside of the vacuum vessel 5 is maintained in a vacuum state and vacuum insulated by the vacuum insulation layer 6.
The band-pass filter 2 and the low noise amplifier 3 sealed into the vacuum vessel 5 are cooled to an extremely low temperature of 70 [K], for example, by the refrigerator 7.
The refrigerator 7, available on the market, is configured so as to be capable of maintaining the temperature of about 70 [K] for a long period of time utilizing a heat exchange cycle by compression/expansion of helium gas or a like.
As described, heat noise generated in the band-pass filter 2 and the low noise amplifier 3 can be reduced by cooling them to the extremely low temperature. As a result, since a noise factor of the radio receiver is significantly improved, receiving sensitivity is greatly improved. Therefore, if this radio receiver is used, effects can be obtained such that a receiving output can be obtained relative to a low level receiving signal on a specified C/N (carrier-to-noise ratio), and transmission power of a transmitter necessary for obtaining the receiving output having the specified C/N does not need to be large. Note that the radio receiver is installed outside or in a vicinity of a top of an antenna tower in many cases to reduce a loss occurred until the receiving signal is input to the antenna terminal 1.
It is required that the vacuum vessel is maintained in the vacuum state for vacuum insulation. On the other hand, the radio receiver needs to be small size and light weight to make construction easy when it is installed outside or in the vicinity of the top of the antenna tower in order to use it as a base station of a mobile communication, for example. Accordingly, it is not desirable to provide the radio receiver with a vacuum pump for constantly vacuum exhausting the inside of the vacuum vessel 5. Furthermore, it is not desirable to externally use the vacuum pump requiring periodical maintenance, because an operation cost for providing a communication service increases due to shortening of a maintenance interval.
Therefore, a getter material 12 that controls an increase of gas pressure inside the vacuum insulation layer 6 is generally provided in the vacuum vessel 5 as means for maintaining the inside of the vacuum vessel 5 in the vacuum state. The getter material 12 capable of adsorbing especially hydrogen gas is used in many cases. This is because gas ejected inside the vacuum insulation layer 6 contains much hydrogen gas since the vacuum vessel 5 is manufactured of stainless steel to which surface treating has been performed. Further, the getter material 12 is subject to heat treating in vacuum by a temperature determined according to its type. After this treating, a clean and activated alloy metal surface capable of adsorbing a large amount of gas is exposed, and thus gas adsorption can be started. For this purpose, the getter material 12 has a heater 13 for activation built therein and includes terminals for heater 14 and 15 for electrification.
As such a getter material, a getter material available in the market such as HS404 or HS405 (trade names of Japan Getters Co.) having a Zr (zirconium) alloy as a main component, for example, can be used. Instead of the getter material having a Zr (Zirconium) alloy as a main component, a getter material made up of an alloy that mainly contains Ba (Barium), Ti (Titanium) or V (Vanadium) may be used.
Moreover, the getter material 12 can continuously adsorb the gas by performing heating activation treating again even if the surface for adsorbing gas is saturated by the gas adsorbed. The heating activation treating is performed not only to discharge a portion of the gas adsorbed on the surface of the getter material 12 but also to take in a portion of the gas from a surface layer into the getter material 12. Accordingly, the surface can further adsorb the gas by an amount of the gas taken into the getter material 12.
In addition, the inside of the vacuum vessel 5 is generally cooled to the extremely low temperature of about 70 [K], for example. Specifically, a gas adsorption material 16 such as activated carbon is attached to the cooling stage 8, and it is functioned as a mechanism to control the increase of the gas pressure inside the vacuum insulation layer 6 by the use of agglutination and capture effect of gas that becomes conspicuous at a low temperature. When these treatments have been performed, it is known that the gas pressure inside the vacuum insulation layer 6 can be sufficiently maintained at a low level in a range where no problem occurs for as long as about ten years even if the refrigerator 7 is continuously operated maintaining the low temperature by the treatment.
The getter material 12 is activated before vacuum sealing of the vacuum insulation layer 6. Thereafter, there is a case where the refrigerator 7 is stored in an ambient temperature for as long as two months or more without operation causing the gas pressure inside the vacuum insulation layer 6 to be increased. Also, there is a case where the refrigerator 7 stops operation to increase temperature due to a power outage or a like, and thus the gas captured by the gas adsorption material 16 is discharged into the vacuum insulation layer 6. However, in these cases, there often occur troubles that cooling cannot be performed even if the refrigerator 7 is activated, because a large amount of heat flowed in due to deterioration of the vacuum insulation.